Sponge:In a small bowl, combine the warm water and 2 teaspoons sugar. Stir to dissolve. Stir in the yeast and 1/2 cup flour. Cover with plastic wrap and set aside until bubbly and active, about 10 to 15 minutes.

Dough:In a large bowl, combine the sponge, yogurt, butter, eggs, sugar, salt, and vanilla. Add the flour 1 cup at a time, mixing until the dough comes away cleanly from the sides of the bowl. Turn the dough out onto a lightly floured surface and, adding only enough flour to keep the dough from sticking to your hands or the work surface, knead the dough about 5 minutes, until soft and pliable but not sticky. Let the dough rest while you clean and grease the bowl. Finish kneading the dough until its smooth, supple, and springy.

Place the dough in a greased bowl, turn to coat all surfaces, cover with plastic wrap and a clean towel, and let sit in a warm place for about 1 1/2 hours, or until doubled.

Gently deflate the dough and cover with plastic wrap and let rest on a lightly floured surface for 15 minutes. Make the cinnamon filling by whisking together the sugar, cinnamon, and flour.

Special tip: Brush the dough lightly with milk before spreading on the filling. As the rolls bake, the protein in the milk acts like glue keeping the filling from oozing out.

Divide the dough in half, working with one half at a time, roll out the dough into a 10 x 14 rectangle and spread filling over dough, leaving 1-inch clear along the edges. Roll up the dough into a log the long way.

Special tip: Use dental floss to make accurate, even slices. Its strong and slides through soft dough without compressing the layers or distorting the filling! Wrap the floss ends around the dough until they cross, pull both ends and the floss will slice cleanly through the dough. Divide the log of dough in half first, then those halves in half, continuing in this manner until you have eight or nine equal-sized rolls. Loosely place the rolls in a lightly greased 9 round or square pan and cover with plastic wrap and let rise about 45 minutes. Repeat process with the other half of dough.

Preheat oven to 350°F. Bake until golden brown, about 20 to 25 minutes or to an internal temperature of 190°F. If you're going to serve the rolls immediately, make the icing while the rolls are baking. Combine the sugar and vanilla; add enough cream or milk to make the icing spread-able. Remove the rolls from the oven, and loosen their edges with a knife. Turn them out of the pan onto a rack. To enjoy right away, spread with the icing and serve.

To serve the rolls later, allow them to cool completely, then wrap in plastic wrap and store at room temperature for up to 3 days. Fifteen minutes before you're ready to serve, preheat the oven to 350°F. Unwrap the rolls, place them on an ungreased baking sheet, and tent lightly with aluminum foil. Bake for 10 to 15 minutes, until they're nicely warmed. While the rolls are reheating make the icing. Remove from the oven and spread with the icing. Serve immediately. Enjoy!